Traditionally, a vehicle—such as a car or a heavy road vehicle, but also a rail vehicle—is service braked by means of fluid actuated brake cylinders or actuators. The fluid is normally pressurized air for heavier road vehicles and hydraulic oil for lighter road vehicles.
For different reasons, much development work is presently devoted to designing brake systems where rotative brake energy, normally from electric motors, is transformed into linear, brake applying movements of brake linings or the like, cooperating with brake discs or brake drums of the vehicle.
For emergency and parking brake purposes a so called spring brake actuator can traditionally be connected to the service brake actuator. A powerful spring therein is normally held loaded or energized, and its energy can be released, normally through the service brake actuator, for the above purposes.
In each service brake arrangement the service brake actuator, i.e. in the present case the electric motor, has to be dimensioned for maximum brake applications, even used repeatedly during a short time span, but is normally only needed for delivering considerably less energy at normal brake applications. Investigations show in fact that maximum brake applications occur rarely.
The dimensions of the brake arrangements in the vehicle chassis are often critical, and it is accordingly desirable to minimize the dimension also of the service brake actuator.
The main object of the invention is thus to minimize the dimension of the service brake actuator without impairing the possibility to attain maximum brakings when needed.